The invention relates to a method and an apparatus for applying an additive, preferably a liquid additive, to a moving, spread-out filter material web used in the tobacco-processing industry with at least one spreading element. The invention further relates to an apparatus for producing filter rods for rod-shaped articles of the tobacco-processing industry.
During the production of filter rods used in the tobacco-processing industry, filter tow generally comprising cellulose acetate is pulled from a supply as a running web and is treated. Generally, the filter tow includes a woven material of loosely adhering threads which are pulled apart in order to form a wide and mostly level web such that the threads are moved side-by-side and essentially parallel to each other. The web is spread out inside a spreading nozzle. Following the spreading operation, an additive is supplied to the web. The additive is typically liquid and includes, for example, distributed triacetin drops. The drops dissolve the threads such that these threads permanently stick together, i.e., the threads are interlaced. The threads are then gathered to form a round rope and encased with a filter paper strip in a filter-rope machine. An additive embodied as a finely dispersed powdery substance can also be used in place of a liquid additive. Processing equipment of the type as described in the above is disclosed in U.S. Pat. Nos. 5,060,664 and 4,511,420.
The spraying of plasticizer onto filter tow with the aid of a row of nozzles, arranged transverse to the movement direction of the filter tow, is disclosed in German patent document DE-A-199 59 034. In this process, individual nozzles are controlled with sensors that record the density of the filter tow in the respective sections.
It is vitally important for the quality of the processing that the individual threads or fibers are well separated and that the plasticizer particles are applied evenly.